JP7367369B2 - Humidifying hollow fiber membrane and humidifying hollow fiber membrane module using the same - Google Patents

Description

The present invention relates to a humidifying hollow fiber membrane and a humidifying hollow fiber membrane module. More specifically, the present invention relates to a humidifying hollow fiber membrane and a humidifying hollow fiber membrane module suitably used in a humidifying device used in a fuel cell system.

Hollow fiber membranes are widely used in medical applications such as blood purifiers for patients with renal failure, and water treatment applications such as water purifiers. In addition, since it has pores large enough to allow gas separation, it exhibits excellent gas separation performance among various inorganic membranes, and can be used even in environments where chemical resistance and heat resistance are required. For this reason, in recent years, the use of hollow fiber membranes for humidification for humidifying the diaphragms of fuel cell stacks using hollow fiber membranes has been expanding.

A humidifying hollow fiber membrane for humidifying the diaphragm of a fuel cell stack can be produced from a spinning stock solution made of a water-soluble organic solvent solution of polysulfone resin and hydrophilic polyvinylpyrrolidone, as disclosed in Patent Document 1, for example. A hollow fiber membrane has been proposed. Such hollow fiber membranes do not significantly decrease in elongation even after being immersed in 95° C. hot water for 280 hours, and are therefore excellent in membrane strength and durability.

Here, since fuel cells generally tend to have better power generation efficiency when operated under high temperature conditions, they are required to maintain performance under high temperature environments of, for example, 110°C. Therefore, the humidifying hollow fiber membrane incorporated in the fuel cell system is required to exhibit its performance under such temperature conditions.

However, the hollow fiber membranes for humidification that have been proposed in the past have tended to have lower water vapor permeability as the environment in which they are used shifts to higher temperatures and lower humidity. This tendency is thought to be caused by, for example, the fact that the hydrophilicity of polyvinylpyrrolidone, which is used as a component of the spinning dope for hollow fiber membranes, decreases under high temperature and low humidity environments. Therefore, further improvements are required so that performance can be maintained even in environments of use under high temperature and low humidity.

Patent Document 2 discloses 3 in which a copolymer polymer consisting of hydrophilic units and hydrophobic units is added to a polymer consisting only of hydrophilic units and a polymer consisting only of hydrophobic units, which are the main raw materials for hollow fiber membranes. A hollow fiber membrane composed of the following components is described. However, the above method is a means for achieving blood compatibility of the hollow fiber membrane and suppression of adhesion of proteins and organic substances to the hollow fiber membrane surface, and does not focus on water vapor permeability as in the present invention. .

Further, Patent Document 3 describes a method of increasing water vapor permeability by providing a finger void structure in the cross section of a hollow fiber membrane by controlling the phase separation rate during membrane formation. However, using only the above method, although water vapor permeability can be increased, air barrier properties may not be able to be sufficiently controlled.

Patent No. 4100215 Patent No. 6036882 JP2009-226397A

An object of the present invention is to provide a hollow fiber membrane for humidification that can achieve high water vapor permeability even when the operating temperature is high, and a hollow fiber membrane module thereof.

In order to achieve the above object, the present invention consists of the following configuration.
1. A humidifying hollow fiber membrane, wherein at least a portion of the surface of the humidifying hollow fiber membrane is coated with a copolymer consisting of a hydrophilic unit and a hydrophobic unit.
2. 2. The humidifying hollow fiber membrane according to 1 above, wherein the hydrophobic unit includes at least one type of vinyl carboxylate unit.
3. 3. The humidifying hollow fiber membrane according to any one of 1 to 2 above, wherein the hydrophilic unit includes a vinylpyrrolidone unit.
4. When air at a temperature of 25°C and a pressure of 50 kPa is applied from the inside to the outside of a dry humidifying hollow fiber membrane, the air permeation rate is 2.5 mL/min/cm ² /MPa or more and 300 mL/min/cm ² / The humidifying hollow fiber membrane according to any one of 1 to 3 above, which has a pressure of MPa or less.
5. 5. The humidifying hollow fiber membrane according to any one of 1 to 4 above, which has a finger void structure when the membrane structure in a cross-sectional direction perpendicular to the longitudinal direction of the hollow fiber membrane is observed at a magnification of 1000 times using an electron microscope.
6. 6. The hollow fiber membrane for humidification according to any one of 1 to 5 above, wherein the content of polyvinylpyrrolidone in the hollow fiber membrane is 5% or less.
7. 7. The humidifying hollow fiber membrane according to any one of 1 to 6 above, wherein the hollow fiber membrane has an inner diameter of 500 μm or more and 1000 μm or less, and a membrane thickness of 60 μm or more and 200 μm or less.
8. 8. The humidifying hollow fiber membrane according to any one of 1 to 7 above, wherein the humidifying hollow fiber membrane is made of a polysulfone polymer.
9. A hollow fiber membrane module equipped with the humidifying hollow fiber membrane according to any one of 1 to 8 above.

The humidifying hollow fiber membrane obtained by the present invention can be effectively used as a humidifying hollow fiber membrane with excellent water vapor permeability, and even when the operating temperature is high, for example, at 110 ° C., the humidifying hollow fiber membrane and It is possible to provide excellent effects such as a small decrease in performance as a hollow fiber membrane module.

FIG. 3 is a diagram illustrating an example of a method for measuring the aspect ratio of finger voids. FIG. 2 is a cross-sectional view (enlarged) of a humidifying hollow fiber membrane in which a void exists in the center of the wall thickness. This is a method of measuring water vapor permeability. This method measures the air permeation rate (air barrier property) when dry air is passed through a hollow fiber membrane module.

The humidifying hollow fiber membrane of the present invention is characterized in that at least a portion of the surface of the humidifying hollow fiber membrane is coated with a copolymer consisting of a hydrophilic unit and a hydrophobic unit.

In the present invention, the unit refers to a repeating unit in a (co)polymer obtained by polymerizing monomers. For example, a hydrophobic unit refers to a repeating unit in a (co)polymer obtained by polymerizing a hydrophobic monomer. Moreover, the vinyl carboxylate unit refers to a repeating unit in a (co)polymer obtained by polymerizing a vinyl carboxylate monomer.

In the present invention, a hydrophobic unit is defined as a repeating unit that is sparingly soluble or insoluble in water when used alone as a polymer (having a number average molecular weight of 30,000 or more and 50,000 or less). Here, "poorly soluble" or "insoluble" in water means that the solubility in 100 g of pure water at 20° C. is 1 g or less.

In addition, the hydrophilic unit is defined as a repeating unit that is an independent polymer (having a number average molecular weight of 30,000 or more and 50,000 or less) that is easily soluble in water. Here, "easily soluble in water" means that the solubility in 100 g of pure water at 20° C. exceeds 1 g.

Examples of the hydrophilic unit include, but are not limited to, repeating units provided by monomers such as methacrylic acid, acrylic acid, 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, vinylpyrrolidone, vinyl alcohol, and ethylene glycol. Among these, repeating units provided by vinylpyrrolidone are preferred because they are easily balanced with hydrophobic units.

When the copolymer is introduced onto the surface of the humidifying hollow fiber membrane of the present invention, the hollow fiber membrane is immersed in an aqueous solution containing the copolymer, or the copolymer is introduced into the module equipped with the hollow fiber membrane, which will be described later. A method in which an aqueous solution in which the copolymer is dissolved is passed is preferred. At this time, if the concentration of the copolymer in the aqueous solution is too low, a sufficient amount of the copolymer will not be introduced onto the surface. Therefore, the copolymer concentration in the aqueous solution is preferably 10 ppm or more, more preferably 100 ppm or more, and even more preferably 300 ppm or more. However, if the concentration of the copolymer in the aqueous solution is too high, there is a concern that eluates from the hollow fiber membrane will increase. More preferred. Here, the surface of the hollow fiber membrane means both the outer surface and the inner surface of the hollow fiber.

If the copolymer is poorly soluble or insoluble in water, use an organic solvent that does not dissolve the hollow fiber membrane, or a mixed solvent of water and an organic solvent that is compatible with water and does not dissolve the hollow fiber membrane. The copolymer may be dissolved. Specific examples of organic solvents that can be used as the organic solvent or mixed solvent include alcoholic solvents such as methanol, ethanol, and propanol, but are not limited thereto.

In order to prevent the copolymer introduced into the membrane surface from eluting during use, the humidifying hollow fiber membrane of the present invention is subjected to radiation irradiation or heat treatment after contacting the membrane surface with an aqueous solution containing the copolymer. , it is preferable to insolubilize the copolymer. For the radiation irradiation, α rays, β rays, γ rays, X rays, ultraviolet rays, electron beams, etc. can be used.

In the humidifying hollow fiber membrane of the present invention, when the copolymer is introduced onto the membrane surface, the radiation dose is preferably 15 kGy or more, more preferably 25 kGy or more. This is because 15 kGy or more is effective for stably introducing the copolymer onto the membrane surface. Further, the irradiation dose is preferably 100 kGy or less. If the irradiation dose exceeds 100 kGy, the copolymer is likely to undergo three-dimensional crosslinking and decomposition of the ester group portion of the vinyl carboxylate unit, making it difficult to achieve both water vapor permeability and air barrier properties. be.

In the present invention, an antioxidant may be used to suppress the crosslinking reaction during irradiation with radiation. Antioxidants are molecules that have the property of readily donating electrons to other molecules. Specific examples include, but are not limited to, water-soluble vitamins such as vitamin C, polyphenols, and alcoholic solvents such as methanol, ethanol, and propanol. These antioxidants may be used alone or in combination of two or more. Furthermore, the treatment by radiation irradiation may be used before the step of incorporating the hollow fiber membrane into the module, or may be used after the step of incorporating the hollow fiber membrane into the module.

The hydrophobic unit includes at least one type of vinyl carboxylate unit. The number of carbon atoms at the end of the side chain of the vinyl carboxylate unit is 1 or more and 7 or less. Here, the number of carbon atoms at the end of the side chain refers to the number of carbon atoms in the terminal hydrocarbon group bonded to the carbonyl carbon atom of the side chain ester bond of the vinyl carboxylate unit. For example, the number of carbon atoms at the end of the vinyl acetate unit is 1. In other words, the carbon number of 2 refers to vinyl propanoate. The terminal hydrocarbon group has not only a linear structure but also a branched structure such as an isopropyl group or a tert-butyl group, a cyclic structure such as a cyclohexyl group or a phenyl group, and a heterostructure such as a nitrogen atom or an oxygen atom. May contain atoms. The number of carbon atoms at the end of the side chain of the vinyl carboxylate unit is 1 or more and 7 or less, preferably 2 or more and 6 or less, and more preferably 2 or more and 4 or less. This makes it possible to control the adsorption of the copolymer to the surface of the humidifying hollow fiber membrane and the mobility of the adsorbed water, thereby achieving both water vapor permeability and air barrier properties of the humidifying hollow fiber membrane at high temperatures. becomes possible.

If the number of carbon atoms at the end of the side chain of the vinyl carboxylate unit is too large, the hydrophobicity of the entire copolymer will become stronger, making it easier to repel water. In addition, if the number of carbon atoms at the end of the side chain is 0, it becomes difficult to introduce it to the surface of the humidifying hollow fiber membrane. More preferable vinyl carboxylates used in the vinyl carboxylate unit are vinyl acetate (1 carbon number), vinyl propanoate (2 carbon atoms), vinyl butyrate (3 carbon atoms), and vinyl pentanoate (4 carbon atoms). , vinyl pivalate (4 carbon atoms).

In the copolymer, the mole fraction of the hydrophilic unit to the entire copolymer is preferably 30% or more and 90% or less, more preferably 40% or more and 80% or less, and 50% or more and 70%. It is more preferable that it is the following. The range may be a combination of any of the above upper and lower limits. If the molar fraction of the hydrophilic unit is too small, the hydrophobicity of the entire copolymer will become strong, making it easier for the humidifying hollow fiber membrane to repel water. On the other hand, if it is too large, the hydrophilicity of the entire copolymer becomes strong, the mobility of adsorbed water around the copolymer becomes low, and it becomes difficult to maintain water vapor permeability at high temperatures.

Examples of the arrangement of hydrophilic units and hydrophobic units in the copolymer include graft copolymers, block copolymers, alternating copolymers, and random copolymers. The copolymer can be synthesized, for example, by a chain polymerization method typified by a radical polymerization method using an azo initiator, but the synthesis method is not limited to this.

The amount of the copolymer introduced onto the membrane surface of the humidifying hollow fiber membrane of the present invention can be quantified by total reflection infrared spectroscopy (ATR-IR), as described below. Furthermore, if necessary, it can also be quantified by X-ray electron spectroscopy (XPS) or the like. Here, the membrane surface refers to the outer surface of the hollow fiber membrane with which water vapor comes into contact.

In the present invention, when quantifying the surface introduction amount of a copolymer containing a carboxylic acid vinyl unit as a hydrophobic unit by ATR-IR, the copolymer carboxyl group near 1730 cm-1 is measured at three different locations on the membrane surface. The ratio of the infrared absorption peak area (AC=O) derived from the ester group C=O of the acid vinyl unit to the infrared absorption peak area (AC=C) derived from the benzene ring C=C of polysulfone near 1580 cm Calculate AC=O)/(AC=C). Measurements are taken at three arbitrary locations on the same hollow fiber membrane, and the average value is taken as the amount of copolymer introduced onto the surface. In the present invention, if a homopolymer consisting only of hydrophilic units without vinyl carboxylate units is used, or if the hollow fiber membrane is not coated with a polymer in the first place, copolymer polymers near 1730 cm The infrared absorption peak area (AC=O) derived from the ester group C=O of the combined vinyl carboxylic acid unit is not detected. Therefore, by the above measurement method, it can be seen that the surface of the hollow fiber membrane is not coated with the copolymer consisting of a hydrophilic unit and a hydrophobic unit. Note that ATR-IR can measure surfaces up to a depth of several micrometers.

In the present invention, in order to achieve both water vapor permeability and air barrier properties of the humidifying hollow fiber membrane, the amount of copolymer introduced into the surface is preferably 0.01 or more, more preferably 0.04 or more. It is preferably 0.08 or more, and more preferably 0.08 or more.

By using the copolymer, the humidifying hollow fiber membrane of the present invention can achieve both water vapor permeability and air barrier properties at high temperatures. Therefore, when the humidifying hollow fiber membrane of the present invention is used in a fuel cell system that requires high temperature operation, its effects can be clearly confirmed.

The humidifying hollow fiber membrane of the present invention has an air permeation rate of 2.5 mL/min/cm ² when air at a temperature of 25° C. and a pressure of 50 kPa is applied from the inside to the outside of the dry humidifying hollow fiber membrane. /MPa or more and 300 mL/min/cm ² /MPa or less.

It is preferable that the air permeation rate is 2.5 mL/min/cm ² /MPa or more from the viewpoint of reducing the temperature dependence of the water vapor recovery rate. On the other hand, when the air permeation rate is 300 mL/min/cm ² /MPa or less, when applied to a fuel cell system, it is preferable from the viewpoint of suppressing increase in fuel supply amount due to loss of supplied fuel at startup.

From the viewpoint of increasing the water vapor permeability of the humidifying hollow fiber membrane, it is more preferable that the air permeation rate is 5.0 mL/min/cm ² /MPa or more. On the other hand, from the viewpoint of being applicable to fuel cell stacks with a wide range of specifications by reducing the loss of supplied fuel, it is more preferably 250 mL/min/cm ² /MPa or less.

The hollow fiber membrane for humidification of the present invention has a finger void structure when the membrane structure in a cross-sectional direction perpendicular to the length of the hollow fiber membrane is observed at a magnification of 1000 times using an electron microscope. In the present invention, a finger void refers to a hole that looks like a thumbprint left by a person, and more specifically, when the above observation is performed, the area of the largest void on the inner surface portion and the outer surface portion is (Circular area when the diameter is the maximum length of the void part in a cross-sectional photograph perpendicular to the length of the hollow fiber membrane). Furthermore, the hollow fiber membrane structure having this finger void is referred to as a finger void structure.
As for the shape of a finger void, for example, as shown in Fig. 1, the line that divides one finger void into two from the inner surface to the outer surface is defined as the X-axis 10, and the length of the X-axis at this time and the The length of the Y-axis 20, which is a perpendicular line, is preferably 1.1 times or more, and more preferably 1.5 times or more, the length of the X-axis.

The membrane structure of a humidifying hollow fiber membrane in the transverse cross section is an asymmetric structure in which the membrane pore diameter increases sequentially from the inner surface to the outer surface or from the outer surface to the inner surface, and the resistance to water vapor transmission (diffusion) increases. Permeability decreases. Furthermore, for a target structure (homogeneous membrane) with the same membrane pore size from the inner surface to the outer surface, the selective permeability (air barrier property) is low, and it is difficult to achieve both water vapor permeability and air barrier property. The humidifying hollow fiber membrane of the present invention has a smaller pore size in the innermost surface portion and the outermost surface portion than in the finger void portion, and has a finger void structure in the central portion, thereby improving water vapor permeability. be.

The number of finger voids in the transverse cross section of the humidifying hollow fiber membrane is preferably 3 or more, more preferably 5 or more, per 12,000 μm ² of the observation field when observed with an electron microscope at a magnification of 1000 times. If the number of finger voids is less than three, it may not be possible to expect an improvement in water vapor permeability, which is a characteristic of the finger void structure during hollow fiber membrane production. Further, even if the number of finger voids is too large, the pressure resistance of the hollow fiber membrane may be reduced, so the number is preferably 30 or less, and more preferably 20 or less.

The humidifying hollow fiber membrane of the present invention preferably has an inner diameter of 500 μm or more and 1000 μm or less. If it is less than 500 μm, when a high flow rate of air is flowed through the hollow portion of the hollow fiber membrane, the pressure from the inlet to the outlet of the hollow portion will increase, and in the worst case, the hollow fiber membrane may break. On the other hand, if it exceeds 1000 μm, in a module equipped with a humidifying hollow fiber membrane, the flow of air outside the humidifying hollow fiber membrane may be biased, and the hollow fiber membrane may not be utilized effectively. Furthermore, if the hollow fiber membrane becomes too thick, the size of the module tends to increase, which is not suitable for space saving. Therefore, the inner diameter is preferably 500 μm or more and 1000 μm or less.

Further, the film thickness is preferably 60 μm or more and 200 μm or less. When the membrane thickness is 60 μm or less, the breaking strength of the hollow fiber membrane decreases, and when a high flow rate of air is applied, the hollow fiber membrane may break. Further, if the membrane thickness exceeds 200 μm, the structural control stability during the formation of the hollow fiber membrane may be lacking, and the reproducibility of the membrane formation in the void portion of the hollow fiber membrane may be poor.

The materials constituting the humidifying hollow fiber membrane of the present invention are not particularly limited, but include polysulfone polymers, polystyrene, polyurethane, polyethylene, polypropylene, polycarbonate, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, and polyvinyl chloride. , polyester, etc., but are not limited thereto. Among these, polysulfone-based polymers and polymethyl methacrylate are preferably used because they are easy to form hollow fiber membranes, and the copolymers, ie, ester group-containing polymers, are easy to introduce onto the surface of humidifying hollow fiber membranes.

In the present invention, it is more preferable that the main raw material of the humidifying hollow fiber membrane is a polysulfone polymer. Here, the polysulfone-based polymer is a polymer having an aromatic ring, a sulfonyl group, and an ether group in the main chain, and includes polysulfone, polyphenylsulfone, polyethersulfone, polyallylethersulfone, and the like. Further, the main raw material refers to a raw material that is contained in an amount of 90% by weight or more based on the entire polysulfone polymer.

As the main raw material for the humidifying hollow fiber membrane in the present invention, for example, polysulfone polymers represented by the following chemical formulas (1) and/or (2) are preferably used, but the invention is not limited to these. . n in the formula is an integer of 1 or more, preferably 50 to 80. Note that when n has a distribution, its average value is set to n.

The polysulfone-based polymer that can be used in the humidifying hollow fiber membrane of the present invention is preferably a polymer consisting only of repeating units represented by the above formula (1) and/or (2), but the effects of the present invention cannot be improved. It may be copolymerized with other monomers or modified as long as it does not interfere. When copolymerized with other monomers, the copolymerization ratio of the other monomers is preferably 10% by weight or less based on the entire polysulfone polymer.

Specific examples of polysulfone polymers that can be used in the humidifying hollow fiber membrane of the present invention include Udel polysulfone P-1700, P-3500 (manufactured by Solvay), Ultrason S3010, P3010, S6010 (manufactured by BASF). , Victrex (manufactured by Sumitomo Chemical Co., Ltd.), Radel A (manufactured by Solvay), and Ultrason E (manufactured by BASF).

There are various methods for manufacturing the hollow fiber membrane module of the present invention depending on its use, but the general steps include the process of manufacturing a humidifying hollow fiber membrane, and the process of manufacturing the humidifying hollow fiber membrane into a module. It can be divided into the process of incorporating.

When using a polysulfone polymer as a material constituting the humidifying hollow fiber membrane of the present invention, it is preferable that a hydrophilic polymer is included. Hydrophilic polymers include polyalkylene oxide, polyvinyl alcohol, polyethylene glycol, polyvinylpyrrolidone, etc. Among these, hydrophilic polymers with a glass transition point higher than 150°C are hollow fiber membranes for humidification that have excellent heat resistance. It is used because it can give The exemplified polyvinylpyrrolidone has excellent compatibility with polysulfone-based polymers and has a high glass transition point of 180° C., so it is preferable for use in hollow fiber membranes for humidification.

The polyvinylpyrrolidone added as the hydrophilic polymer has a weight average molecular weight of about 10,000 (equivalent to K-15) to 1,200,000 (equivalent to K-90), preferably 10% by weight per 100% by weight of the polysulfone polymer. It is used in a proportion of ~80% by weight, more preferably 15~60% by weight. When the amount is less than 10% by weight based on the polysulfone polymer, hydrophilicity cannot be imparted to the membrane surface, and there is a concern that the affinity with water vapor may decrease. If it exceeds 80% by weight, the strength of the hollow fiber membrane may be low, making it difficult to form the membrane. In the humidifying hollow fiber membrane of the present invention, the polyvinylpyrrolidone content in the hollow fiber membrane is preferably 5% or less, more preferably 4% or less. When the content of polyvinylpyrrolidone in the hollow fiber membrane is 5% or more, the hydrophilicity or swelling property of polyvinylpyrrolidone decreases as the usage environment becomes high temperature and/or low humidity. Maintaining performance may be difficult. The polyvinylpyrrolidone content in the hollow fiber membrane is measured as described in Example (4) below.

The hollow fiber membrane module of the present invention is suitably used as a fuel cell system. An example of a method for manufacturing a hollow fiber membrane module used in a fuel cell system will be shown.

As a method for manufacturing a humidifying hollow fiber membrane built into a hollow fiber membrane module, there is the following method. That is, polysulfone and polyvinylpyrrolidone (weight ratio preferably 20:1 to 1:5, more preferably 5:1 to 1:1) are mixed with a good solvent for polysulfone (N,N-dimethylacetamide, dimethylsulfoxide, dimethylformamide, N - Methylpyrrolidone, dioxane, etc.) and a poor solvent are dissolved in a mixed solution (concentration is preferably 10 to 30% by weight, more preferably 15 to 25% by weight) when discharging from a double annular mouthpiece. The injection liquid is poured inside the tube, and after running through the dry section, it is led to the coagulation bath. At this time, since the humidity in the dry section has an effect, water replenishment from the outer surface of the membrane during running in the dry section accelerates the phase separation behavior near the outer surface and expands the pore size, resulting in a reduction in permeation during humidification. It is also possible to reduce the resistance. However, if the relative humidity is too high, coagulation of the stock solution on the outer surface becomes dominant, and the pore diameter tends to become smaller, resulting in an increase in permeation resistance during humidification. Therefore, the relative humidity is preferably 60 to 90%. Further, as the composition of the injection solution, it is preferable to use one based on the solvent used in the stock solution from the viewpoint of process suitability. For example, when dimethylacetamide is used, an aqueous solution having a concentration of 30 to 70% by weight, more preferably 40 to 60% by weight is preferably used.

The method for incorporating the humidifying hollow fiber membrane of the present invention into a module is not particularly limited, but an example is as follows. First, the hollow fiber membranes are cut to the required length, the required number of membranes are bundled, and then placed in a cylindrical case. After that, temporarily cap both ends and add potting agent to both ends of the hollow fiber membrane. At this time, a method of adding the potting agent while rotating the module with a centrifuge is a preferred method because the potting agent is filled uniformly. After the potting agent is solidified, both ends of the hollow fiber membrane are cut so that both ends are open to obtain a hollow fiber membrane module.

In the present invention, the polysulfone-based polymer used as the main raw material for the humidifying hollow fiber membrane is generally highly hydrophobic, so if it is used as a humidifying hollow fiber membrane as it is, water vapor will be easily repelled on the membrane surface. Therefore, in the hollow fiber membrane module of the present invention, a humidifying hollow fiber membrane in which the copolymer is introduced into the membrane surface is preferably used. Methods for introducing the copolymer onto the membrane surface include a method in which a solution containing the copolymer is brought into contact with the hollow fiber membrane, a method in which a hollow fiber membrane module is manufactured and then brought into contact with the hollow fiber membrane in the module, During membrane spinning, a membrane forming stock solution containing a copolymer is used. Alternatively, a method may be mentioned in which an injection liquid containing the copolymer is brought into contact with the inside of the hollow fiber.

Further, the humidifying hollow fiber membrane of the present invention is also a water vapor permeable membrane that moves water vapor toward the dry fluid among the fluids flowing inside and outside the hollow fiber membrane. That is, by supplying dry gas (purge gas) to the outside of the hollow fiber membrane and supplying humid gas or water to the inside of the hollow fiber membrane, it is also possible to dehumidify the humid air inside the hollow fiber membrane. Therefore, it can be suitably used for both humidification and dehumidification.

INDUSTRIAL APPLICABILITY The present invention can be used in the field of fuel cells as a hollow fiber membrane module or a humidifying hollow fiber membrane applicable to a fuel cell system. In addition to fuel cell applications, it can also be used in general household humidifiers, dehumidification membranes, and the like.

Next, the present invention will be explained with reference to examples.

(1) Dimensional measurement of hollow fiber membrane The produced hollow fiber membrane was pulled out and the cross section in the longitudinal direction of the hollow fiber was measured with a 200x lens of Micro Watcher (manufactured by KEYENCE, VH-Z100) to determine the inner diameter of the hollow fiber membrane and the membrane. I wanted thickness.

(2) Observation of voids in hollow fiber membrane The membrane structure in the cross-sectional direction perpendicular to the length of one of the hollow fiber membranes produced was observed using an electron microscope at a magnification of 1000 times. Figure 2 shows an example of a photograph of the void area. At this time, it was confirmed whether the voids at the center of the wall thickness of the hollow fiber membrane were larger than the voids near the inner and outer surfaces of the hollow fiber membrane, and whether there was a finger void structure.

(3) Amount of copolymer introduced onto the hollow fiber membrane surface The hollow fiber membrane coated with the copolymer after γ-ray irradiation was cut into a semi-cylindrical shape using a microtome and fixed on a sample stand. The measurement was performed with a viewing angle of 100 μm x 100 μm, which is the range (aperture) of the infrared light, and with the number of integrations being 30 times per point. Ratio between the peak area Ac=c derived from the benzene ring double bond of polysulfone near 1590 cm-1 and the peak area Ac=o derived from the ester bond of the copolymer vinyl carboxylate unit near 1730 cm-1 Ac= o/Ac=c was calculated. Measurements were made at three locations on the same hollow fiber membrane of one module, and the average value was taken as the amount of the copolymer introduced onto the surface of the hollow fiber membrane. The average value was calculated by rounding to the third decimal place.

(4) Measurement of polyvinylpyrrolidone (PVP) content of hollow fiber membrane The hollow fiber membrane was dried in a dryer at 120° C. for 5 hours and cut into lengths of about 5 mm. After weighing this, the nitrogen content based on the hollow fiber membrane in a dry state was measured using an NC analyzer. When the main raw materials for forming a hollow fiber membrane are polysulfone and PVP, the PVP content (X) was calculated from the nitrogen content (N) because nitrogen-derived substances are not included other than PVP. From the obtained PVP content (X), the polysulfone-based PVP content (Y) was calculated.
X: PVP content (%, based on dry hollow fiber membrane) = (N x 111/14) x 100
Y: PVP content (%, based on polysulfone) = [X/(100-X)] x 100.

(5) Measurement of water vapor permeation rate Water vapor permeability was measured as follows. First, the hollow fiber membrane modules were connected as shown in FIG.
Using a hollow fiber membrane module, dry air at a temperature of 60°C and a pressure of 100 kPaG is supplied to the inside of the hollow fiber membrane, and humidity is controlled at a temperature of 100°C, 40% RH, and a pressure of 50 kPaG from the outside of the hollow fiber membrane using a humidifier. Air was passed in a cross flow of one pass, and the amount of water vapor permeation per hour was measured, and the value was calculated in terms of water vapor permeation rate (g/min/cm ² ) per unit membrane area and unit time. After that, the temperature of the dry air flowing inside the hollow fiber membrane was raised to 110°C, and the amount of water vapor permeation per hour was similarly measured, and the water vapor air velocity per unit membrane area and unit time (g/min/ The numerical value was calculated in terms of cm ² ). In addition, the water vapor recovery rate was calculated from the ratio of the water vapor flow rate (g/min) of the humidified air supplied to the outside of the hollow fiber membrane and the water vapor flow rate (g/min) of the air coming out from the inside of the hollow fiber membrane. .

(6) Measurement of air permeation rate
The air permeation rate (air barrier property) when dry air was passed was measured as follows. First, the hollow fiber membrane modules were connected as shown in FIG. The hollow fiber membrane module was dried in a dryer at 50° C. for 24 hours or more and used immediately. Air at a temperature of 25° C. and a pressure of 50 kPa was applied from the inside to the outside of the membrane, the amount of air permeation was measured, and the value was calculated in terms of the amount of air permeation per unit membrane area, unit time, and 1 MPa. At this time, if there is a large amount of air permeation from the inside of the membrane to the outside, the pressure difference between the outside and inside of the membrane will become small, and it may not be possible to accurately measure the amount of air permeation at a pressure of 50 kPa. 150, the pressure outside the membrane was measured, and corrections were made as necessary.

(Synthesis example 1)
A vinyl pyrrolidone/vinyl propanoate random copolymer was produced by the following method. Mixing 19.5 g of vinyl pyrrolidone monomer, 17.5 g of vinyl propanoate monomer, 56 g of t-amyl alcohol as a polymerization solvent, and 0.175 g of 2,2'-azobis(2,4-dimethylvaleronitrile) as a polymerization initiator, The mixture was stirred at 70° C. for 6 hours under a nitrogen atmosphere. The reaction solution was cooled to room temperature to stop the reaction, concentrated, and poured into hexane. The precipitated white precipitate was collected and dried under reduced pressure to obtain 21.0 g of a copolymer. From the results of ¹ H-NMR, the molar fraction of vinylpyrrolidone units was 60%. Further, the number average molecular weight Mn was 16,500 from the GPC measurement results.

(Example 1)
18% by weight of polysulfone ("Udel" P-3500 manufactured by Solvay) and 5 parts by weight of polyvinylpyrrolidone (K30 manufactured by BASF) were dissolved by heating in 76% by weight of N,N-dimethylacetamide and 1% by weight of water to obtain a membrane forming stock solution. And so. A solution containing 45% by mass of N,N-dimethylacetamide and 55% by mass of water was used as the core liquid.

The membrane-forming stock solution was sent to the spinneret and discharged from the outer tube of the orifice-type double tube mouthpiece, and the core solution was discharged from the inner tube. The discharged membrane-forming stock solution passes through a dry zone atmosphere with a dew point of 30°C, is led to a 100% water coagulation bath, and is then passed through a water washing process at 80°C for 100 seconds to form a hollow fiber membrane in a wet state. was rolled up and made into a bundle. The inner diameter of the hollow fiber membrane was 660 μm, and the membrane thickness was 95 μm.

The bundle of wound hollow fiber membranes was divided into 1000 pieces each having a length of 0.3 m in the longitudinal direction, and dried at 50° C. for 24 hours in a dry heat dryer to obtain dry hollow fiber membranes for humidification. When a longitudinal section of the hollow fiber membrane was observed using an electron microscope, a void was observed in the center of the wall thickness. Nine finger void structures were confirmed in an area of 12,000 μm ² .

The obtained dry hollow fiber membrane was immersed in an aqueous solution containing 1,000 ppm of vinyl pyrrolidone/vinyl acetate random copolymer (“KOLLIDON” (registered trademark) VA64 manufactured by BASF) and was irradiated with γ-rays at a dose of 25 kGy. Irradiated. By washing with warm water at 80° C. for 5 hours and drying, a humidifying hollow fiber membrane whose surface was coated with the copolymer was obtained. From the ATR-IR measurement results, it was found that the average amount of copolymer introduced on the surface of the hollow fiber membrane (area ratio) was 0.11.

The hollow fiber membrane for humidification is made of stainless steel with an inner diameter of φ5 so that the effective inner surface area (the surface area of the inner surface of the hollow fiber membrane that is not covered by the potting agent added in the next step) is 20 cm ² . Fill the case, fix both ends of the hollow fiber membrane to the ends of the stainless steel case by potting, and cut a part of the end of the potting agent to open both ends of the hollow fiber membrane, creating a hollow fiber membrane module. It was set to 1.

The air permeation rate and water vapor permeation rate in the obtained hollow fiber membrane module were measured. The results are shown in Table 2. The air permeation rate during drying was 50 mL/cm ² /min/MPa. The rate of performance decrease in water vapor recovery rate from dry air temperature of 60°C to 110°C was 0.9%, and a hollow fiber membrane module with excellent water vapor permeability even at a high temperature of 110°C was obtained.

(Example 2)
Instead of the aqueous solution in which vinyl pyrrolidone/vinyl acetate random copolymer (“KOLLIDON” (registered trademark) VA64 manufactured by BASF) was dissolved, the vinyl pyrrolidone/vinyl propanoate random copolymer synthesized in Synthesis Example 1 (vinyl pyrrolidone unit A hollow fiber membrane module 2 was obtained by carrying out an experiment in the same manner as in Example 1, except for using a 0.5 mass% ethanol aqueous solution in which 750 ppm of (mol fraction: 60%, number average molecular weight: 16,500) was dissolved. The air permeation rate and water vapor permeation rate in the obtained hollow fiber membrane module were measured. The results are shown in Table 2. The air permeation rate during drying was 8 mL/cm ² /min/MPa. The performance deterioration rate of water vapor recovery rate from dry air temperature of 60°C to 110°C was 0.9%, and a hollow fiber membrane module with excellent water vapor permeability even at a high temperature of 110°C was obtained.

(Example 3)
Example 1 except that the concentration of the 0.5% by mass ethanol aqueous solution in which vinylpyrrolidone/vinyl propanoate random copolymer (mole fraction of vinylpyrrolidone unit 60%, number average molecular weight 16,500) was 100ppm. An experiment was conducted in the same manner as above, and a hollow fiber membrane module 3 was obtained.

The air permeation rate and water vapor permeation rate in the obtained hollow fiber membrane module were measured. The results are shown in Table 2. The air permeation rate during drying was 101 mL/cm ² /min/MPa. The rate of performance decrease in water vapor recovery rate from dry air temperature of 60°C to 110°C was 0.4%, and a hollow fiber membrane module with excellent water vapor permeability even at a high temperature of 110°C was obtained.

(Example 4)
18% by weight of polysulfone ("Udel" P-3500 manufactured by Solvay) and 5 parts by weight of polyvinylpyrrolidone (K30 manufactured by BASF) were dissolved by heating in 76% by weight of N,N-dimethylacetamide and 1% by weight of water to obtain a membrane forming stock solution. And so. A solution containing 50% by mass of N,N-dimethylacetamide and 50% by mass of water was used as the core liquid.

The membrane-forming stock solution was sent to the spinneret and discharged from the outer tube of the orifice-type double tube mouthpiece, and the core solution was discharged from the inner tube. The discharged membrane-forming stock solution passes through a dry zone atmosphere with a dew point of 30°C, is led to a 100% water coagulation bath, and is then passed through a water washing process at 80°C for 100 seconds to form a hollow fiber membrane in a wet state. was rolled up and made into a bundle. The inner diameter of the hollow fiber membrane was 660 μm, and the membrane thickness was 95 μm.

The bundle of wound hollow fiber membranes was divided into 1000 pieces each having a length of 0.3 m in the longitudinal direction, and dried at 50° C. for 24 hours in a dry heat dryer to obtain dry hollow fiber membranes for humidification. When a longitudinal section of the hollow fiber membrane was observed using an electron microscope, a void was observed in the center of the wall thickness. Nine finger void structures were confirmed in an area of 12,000 μm ² .

The obtained dry hollow fiber membrane was immersed in an aqueous solution containing 2,000 ppm of vinyl pyrrolidone/vinyl acetate random copolymer (“KOLLIDON” (registered trademark) VA64 manufactured by BASF) and was irradiated with γ-rays at a dose of 25 kGy. Irradiated. By washing with warm water at 80° C. for 5 hours and drying, a humidifying hollow fiber membrane whose surface was coated with the copolymer was obtained. From the ATR-IR measurement results, it was found that the average amount of copolymer introduced on the surface of the hollow fiber membrane (area ratio) was 0.14.

The hollow fiber membrane for humidification is made of stainless steel with an inner diameter of φ5 so that the effective inner surface area (the surface area of the inner surface of the hollow fiber membrane that is not covered by the potting agent added in the next step) is 20 cm ² . Fill the case, fix both ends of the hollow fiber membrane to the ends of the stainless steel case by potting, and cut a part of the end of the potting agent to open both ends of the hollow fiber membrane, creating a hollow fiber membrane module. It was set as 4.

The air permeation rate and water vapor permeation rate in the obtained hollow fiber membrane module were measured. The results are shown in Table 2. The air permeation rate during drying was 51 mL/cm ² /min/MPa. The rate of performance decrease in water vapor recovery rate from 60°C to 110°C was 1.8%, and a hollow fiber membrane module with excellent water vapor permeability even at a high temperature of 110°C was obtained.

(Example 5)
An experiment was conducted in the same manner as in Example 4, except that the concentration of the aqueous solution in which vinyl pyrrolidone/vinyl acetate random copolymer (“KOLLIDON” (registered trademark) VA64 manufactured by BASF) was dissolved was 500 ppm. I got it.

The air permeation rate and water vapor permeation rate in the obtained hollow fiber membrane module were measured. The results are shown in Table 2. The air permeation rate during drying was 204 mL/cm ² /min/MPa. The rate of performance decrease in water vapor recovery rate from 60°C to 110°C in dry air temperature was 1.3%, and a hollow fiber membrane module with excellent water vapor permeability even at a high temperature of 110°C was obtained.

(Example 6)
Instead of the aqueous solution in which vinyl pyrrolidone/vinyl acetate random copolymer (“KOLLIDON” (registered trademark) VA64 manufactured by BASF) was dissolved, the vinyl pyrrolidone/vinyl propanoate random copolymer synthesized in Synthesis Example 1 (vinyl pyrrolidone unit The experiment was carried out in the same manner as in Example 4, except that a 0.5 mass % aqueous ethanol solution containing 1,000 ppm of (mol fraction 60%, number average molecular weight 16,500) dissolved therein was used, and a hollow fiber membrane module 6 was obtained.

The air permeation rate and water vapor permeation rate in the obtained hollow fiber membrane module were measured. The results are shown in Table 2. The air permeation rate during drying was 20 mL/cm ² /min/MPa. The performance deterioration rate of water vapor recovery rate from dry air temperature of 60°C to 110°C was 0.9%, and a hollow fiber membrane module with excellent water vapor permeability even at a high temperature of 110°C was obtained.

(Example 7)
Example 4 except that the concentration of the 0.5% by mass ethanol aqueous solution in which vinylpyrrolidone/vinyl propanoate random copolymer (mole fraction of vinylpyrrolidone unit 60%, number average molecular weight 16,500) was 250ppm. An experiment was conducted in the same manner as in the above, and a hollow fiber membrane module 7 was obtained.

The air permeation rate and water vapor permeation rate in the obtained hollow fiber membrane module were measured. The results are shown in Table 2. The air permeation rate during drying was 228 mL/cm ² /min/MPa. The rate of performance decrease in water vapor recovery rate from dry air temperature of 60°C to 110°C was 0.9%, and a hollow fiber membrane module with excellent water vapor permeability even at a high temperature of 110°C was obtained.

(Example 8)
Example 4 except that the concentration of the 0.5% by mass ethanol aqueous solution in which vinylpyrrolidone/vinyl propanoate random copolymer (mole fraction of vinylpyrrolidone unit 60%, number average molecular weight 16,500) was 100ppm. An experiment was conducted in the same manner as above, and a hollow fiber membrane module 8 was obtained.

The air permeation rate and water vapor permeation rate in the obtained hollow fiber membrane module were measured. The results are shown in Table 2. The air permeation rate during drying was 305 mL/cm ² /min/MPa. The rate of performance decline in water vapor recovery rate from 60°C to 110°C was 1.3%. Although the air permeation rate during drying was high and there was a concern about loss of supplied fuel, a hollow fiber membrane module with excellent water vapor permeability even at a high temperature of 110° C. was obtained. (Example 9)
18% by weight of polysulfone ("Udel" P-3500 manufactured by Solvay) and 5 parts by weight of polyvinylpyrrolidone (K30 manufactured by BASF) were dissolved by heating in 76% by weight of N,N-dimethylacetamide and 1% by weight of water to obtain a membrane forming stock solution. And so. A solution containing 55% by mass of N,N-dimethylacetamide and 45% by mass of water was used as the core liquid.

The membrane-forming stock solution was sent to the spinneret and discharged from the outer tube of the orifice-type double tube mouthpiece, and the core solution was discharged from the inner tube. The discharged membrane-forming stock solution passes through a dry zone atmosphere with a dew point of 30°C, is led to a 100% water coagulation bath, and is then passed through a water washing process at 80°C for 100 seconds to form a hollow fiber membrane in a wet state. was rolled up and made into a bundle. The inner diameter of the hollow fiber membrane was 660 μm, and the membrane thickness was 95 μm.

The wound bundle of hollow fiber membranes was divided into 1000 pieces each having a length of 0.3 m, and dried in a dry heat dryer at 50° C. for 24 hours to obtain dry hollow fiber membranes. When a longitudinal section of the hollow fiber membrane was observed using an electron microscope, a void was observed in the center of the wall thickness. Nine finger void structures were confirmed in an area of 12,000 μm ² .

The obtained dry hollow fiber membrane was immersed in a 0.5% by mass ethanol aqueous solution in which 1500 ppm of the vinyl pyrrolidone/vinyl propanoate random copolymer synthesized in Synthesis Example 1 was dissolved, and then irradiated with γ-rays at a dose of 25 kGy. Irradiated. By washing with warm water at 80° C. for 5 hours and drying, a humidifying hollow fiber membrane whose surface was coated with the copolymer was obtained. The ATR-IR measurement results revealed that the amount of copolymer introduced on the surface of the hollow fiber membrane (area ratio) was 0.16 on average.

The hollow fiber membrane for humidification is made of stainless steel with an inner diameter of φ5 so that the effective inner surface area (the surface area of the inner surface of the hollow fiber membrane that is not covered by the potting agent added in the next step) is 20 ^cm2 . Fill the case, fix both ends of the hollow fiber membrane to the ends of the stainless steel case by potting, and cut a part of the end of the potting agent to open both ends of the hollow fiber membrane, creating a hollow fiber membrane module. It was set as 9.

The air permeation rate and water vapor permeation rate in the obtained hollow fiber membrane module were measured. The results are shown in Table 2.
The air permeation rate during drying was 50 mL/cm2/min/MPa. The rate of performance decrease in water vapor recovery rate from 60°C to 110°C in dry air temperature was 1.8%, and a hollow fiber membrane module with excellent water vapor permeability even at a high temperature of 110°C was obtained.

(Example 10)
An experiment was conducted in the same manner as in Example 9, except that the concentration of the ethanol aqueous solution in which the vinyl pyrrolidone/vinyl propanoate random copolymer was dissolved was 500 ppm, and a hollow fiber membrane module 10 was obtained.

The air permeation rate and water vapor permeation rate in the obtained hollow fiber membrane module were measured. The results are shown in Table 2. The air permeation rate during drying was 252 mL/cm2/min/MPa. The performance deterioration rate of water vapor recovery rate from 60°C to 110°C in dry air temperature was 1.1%, and a hollow fiber membrane module with excellent water vapor permeability even at a high temperature of 110°C was obtained.

(Example 11)
18% by weight of polysulfone ("Udel" P-3500 manufactured by Solvay) and 9 parts by weight of polyvinylpyrrolidone (K30 manufactured by BASF) were dissolved by heating in 72% by weight of N,N-dimethylacetamide and 1% by weight of water to obtain a film forming stock solution. And so. A solution containing 55% by mass of N,N-dimethylacetamide and 45% by mass of water was used as the core liquid.

The membrane-forming stock solution was sent to the spinneret and discharged from the outer tube of the orifice-type double tube mouthpiece, and the core solution was discharged from the inner tube. The discharged membrane-forming stock solution passes through a dry zone atmosphere with a dew point of 30°C, is led to a 100% water coagulation bath, and is then passed through a water washing process at 80°C for 100 seconds to form a hollow fiber membrane in a wet state. was rolled up and made into a bundle. The inner diameter of the hollow fiber membrane was 660 μm, and the membrane thickness was 95 μm.

The bundle of wound hollow fiber membranes is divided into 1000 units of 0.3 m in the longitudinal direction and dried in a dry heat dryer at 50°C for 24 hours to obtain dry hollow fiber membranes (hollow fiber membranes for humidification). Obtained. When a longitudinal section of the hollow fiber membrane was observed using an electron microscope, a void was observed in the center of the wall thickness. Seven finger void structures were confirmed in an area of 12,000 μm ² .

The obtained dry hollow fiber membrane was prepared by dissolving 1000 ppm of the vinyl pyrrolidone/vinyl propanoate random copolymer (mole fraction of vinyl pyrrolidone unit 60%, number average molecular weight 16,500) synthesized in Synthesis Example 1. While immersed in a 5% by mass ethanol aqueous solution, γ-rays were irradiated at a dose of 25 kGy. By washing with warm water at 80° C. for 5 hours and drying, a humidifying hollow fiber membrane whose surface was coated with the copolymer was obtained.

The hollow fiber membrane for humidification is made of stainless steel with an inner diameter of φ5 so that the effective inner surface area (the surface area of the inner surface of the hollow fiber membrane that is not covered by the potting agent added in the next step) is 20 cm ² . Fill the case, fix both ends of the hollow fiber membrane to the ends of the stainless steel case by potting, and cut a part of the end of the potting agent to open both ends of the hollow fiber membrane, creating a hollow fiber membrane module. It was set to 11. The air permeation rate and water vapor permeation rate in the obtained hollow fiber membrane module were measured. The results are shown in Table 2. The air permeation rate during drying was 10 mL/cm ² /min/MPa. The rate of performance decrease in water vapor recovery rate from 60°C to 110°C was 1.3%, and a hollow fiber membrane module with excellent water vapor permeability even at a high temperature of 110°C was obtained.

(Example 12)
Example 11 except that the concentration of the 0.5% by mass ethanol aqueous solution in which vinylpyrrolidone/vinyl propanoate random copolymer (mole fraction of vinylpyrrolidone unit: 60%, number average molecular weight: 16,500) was 500ppm. An experiment was conducted in the same manner as above, and a hollow fiber membrane module 12 was obtained.

The air permeation rate and water vapor permeation rate in the obtained hollow fiber membrane module were measured. The results are shown in Table 2. The air permeation rate during drying was 204 mL/cm ² /min/MPa. The rate of performance decrease in water vapor recovery rate from dry air temperature of 60°C to 110°C was 0.8%, and a hollow fiber membrane module with excellent water vapor permeability even at a high temperature of 110°C was obtained.

(Example 13)
18% by weight of polysulfone ("Udel" P-3500, manufactured by Solvay), 6 parts by weight of polyvinylpyrrolidone (K30, manufactured by BASF), 3 parts by weight of polyvinylpyrrolidone (K90, manufactured by BASF), 72% by weight of N,N-dimethylacetamide, 1% by mass of water was dissolved by heating to obtain a membrane forming stock solution. A solution containing 45% by mass of N,N-dimethylacetamide and 55% by mass of water was used as the core liquid.

The membrane-forming stock solution was sent to the spinneret and discharged from the outer tube of the orifice-type double tube mouthpiece, and the core solution was discharged from the inner tube. The discharged membrane-forming stock solution passes through a dry zone atmosphere with a dew point of 30°C, is led to a 100% water coagulation bath, and is then passed through a water washing process at 80°C for 100 seconds to form a hollow fiber membrane in a wet state. was rolled up and made into a bundle. The inner diameter of the hollow fiber membrane was 660 μm, and the membrane thickness was 95 μm.

The bundle of wound hollow fiber membranes is divided into 1000 units of 0.3 m in the longitudinal direction and dried in a dry heat dryer at 50°C for 24 hours to obtain dry hollow fiber membranes (hollow fiber membranes for humidification). Obtained. When a longitudinal section of the hollow fiber membrane was observed under an electron microscope, no finger void structure was formed.

The obtained dry hollow fiber membrane was dissolved in a 0.2% by mass ethanol aqueous solution containing 50ppm of vinylpyrrolidone/vinyl propanoate random copolymer (mole fraction of vinylpyrrolidone unit 60%, number average molecular weight 16,500). γ-ray irradiation was performed at an irradiation dose of 25 kGy in the immersed state. By washing with warm water at 80° C. for 5 hours and drying, a humidifying hollow fiber membrane whose surface was coated with the copolymer was obtained.

The hollow fiber membrane for humidification is made of stainless steel with an inner diameter of φ5 so that the effective inner surface area (the surface area of the inner surface of the hollow fiber membrane that is not covered by the potting agent added in the next step) is 20 cm ² . Fill the case, fix both ends of the hollow fiber membrane to the ends of the stainless steel case by potting, and cut a part of the end of the potting agent to open both ends of the hollow fiber membrane, creating a hollow fiber membrane module. It was set to 13.

The air permeation rate and water vapor permeation rate in the obtained hollow fiber membrane module were measured. The results are shown in Table 2. The air permeation rate during drying was 0.0 mL/cm ² /min/MPa. The performance deterioration rate of water vapor recovery rate from dry air temperature of 60°C to 110°C was 3.1%, and the hollow fiber membrane module showed a small performance deterioration of water vapor permeability under the high temperature condition of 110°C.

(Comparative example 1)
A hollow fiber membrane module 14 was obtained by conducting the same experiment as in Example 4 except that the copolymer was not used. The air permeation rate in the obtained hollow fiber membrane module was measured. The results are shown in Table 2. The air permeation rate during drying was 330 mL/cm ² /min/MPa. Additionally, water vapor permeability was not measured due to the high air permeation rate of the membrane and the loss of feed air.

(Comparative example 2)
A hollow fiber membrane module 15 was obtained by conducting the same experiment as in Example 9 except that the copolymer was not used. The air permeation rate in the obtained hollow fiber membrane module was measured. The results are shown in Table 2. The air permeation rate during drying was 454 mL/cm ² /min/MPa. Additionally, water vapor permeability was not measured due to the high air permeation rate of the membrane and the loss of feed air.

(Comparative example 3)
The same experiment as in Example 11 was conducted, except that the copolymer was not used, and a hollow fiber membrane module 16 was obtained. The air permeation rate in the obtained hollow fiber membrane module was measured. The results are shown in Table 2. The air permeation rate during drying was 715 mL/cm ² /min/MPa. Additionally, water vapor permeability was not measured due to the high air permeation rate of the membrane and the loss of feed air.

(Comparative example 4)
18% by weight of polysulfone ("Udel" P-3500 manufactured by Solvay) and 9 parts by weight of polyvinylpyrrolidone (K30 manufactured by BASF) were dissolved by heating in 72% by weight of N,N-dimethylacetamide and 1% by weight of water to obtain a film forming stock solution. And so. A solution containing 45% by mass of N,N-dimethylacetamide and 55% by mass of water was used as the core liquid.

The membrane-forming stock solution was sent to the spinneret and discharged from the outer tube of the orifice-type double tube mouthpiece, and the core solution was discharged from the inner tube. The discharged membrane-forming stock solution passes through a dry zone atmosphere with a dew point of 30°C, is led to a 100% water coagulation bath, and is then passed through a water washing process at 80°C for 100 seconds to form a hollow fiber membrane in a wet state. was rolled up and made into a bundle. The inner diameter of the hollow fiber membrane was 660 μm, and the membrane thickness was 95 μm.

The bundle of wound hollow fiber membranes is divided into 1000 units of 0.3 m in the longitudinal direction and dried in a dry heat dryer at 50°C for 24 hours to obtain dry hollow fiber membranes (hollow fiber membranes for humidification). Obtained. When a longitudinal section of the hollow fiber membrane was observed using an electron microscope, a void was observed in the center of the wall thickness. Seven finger void structures were confirmed in an area of 12,000 μm ² .

The hollow fiber membrane for humidification is made of stainless steel with an inner diameter of φ5 so that the effective inner surface area (the surface area of the inner surface of the hollow fiber membrane that is not covered by the potting agent added in the next step) is 20 cm ² . Fill the case, fix both ends of the hollow fiber membrane to the ends of the stainless steel case by potting, and cut a part of the end of the potting agent to open both ends of the hollow fiber membrane, creating a hollow fiber membrane module. It was set at 17. The air permeation rate and water vapor permeation rate in the obtained hollow fiber membrane module were measured. The results are shown in Table 2. The air permeation rate during drying was 0.0 mL/cm ² /min/MPa. The performance deterioration rate of water vapor recovery rate from 60°C to 110°C was 5.3%, and it was confirmed that water vapor permeability performance decreased under the high temperature condition of 110°C.

(Comparative example 5)
The same experiment as in Example 13 was conducted, except that the copolymer was not used, and a hollow fiber membrane module 18 was obtained. The air permeation rate in the obtained hollow fiber membrane module was measured. The results are shown in Table 2. The air permeation rate during drying was 0.0 mL/cm ² /min/MPa. The performance deterioration rate of water vapor recovery rate from dry air temperature of 60°C to 110°C was 5.7%, and a performance deterioration of water vapor permeability was confirmed under the high temperature condition of 110°C.

(Comparative example 6)
18% by weight of polysulfone ("Udel" P-3500 manufactured by Solvay) and 15 parts by weight of polyvinylpyrrolidone (K30 manufactured by BASF) were dissolved by heating in 66% by weight of N,N-dimethylacetamide and 1% by weight of water to obtain a membrane forming stock solution. And so. A solution containing 45% by mass of N,N-dimethylacetamide and 55% by mass of water was used as the core liquid.

The membrane-forming stock solution was sent to the spinneret and discharged from the outer tube of the orifice-type double tube mouthpiece, and the core solution was discharged from the inner tube. The discharged membrane-forming stock solution passes through a dry zone atmosphere with a dew point of 30°C, is led to a 100% water coagulation bath, and is then passed through a water washing process at 80°C for 100 seconds to form a hollow fiber membrane in a wet state. was rolled up and made into a bundle. The inner diameter of the hollow fiber membrane was 660 μm, and the membrane thickness was 95 μm.

The bundle of wound hollow fiber membranes is divided into 1000 units of 0.3 m in the longitudinal direction and dried in a dry heat dryer at 50°C for 24 hours to obtain dry hollow fiber membranes (hollow fiber membranes for humidification). Obtained. When a longitudinal section of the hollow fiber membrane was observed under an electron microscope, no finger void structure was formed.

The hollow fiber membrane for humidification is made of stainless steel with an inner diameter of φ5 so that the effective inner surface area (the surface area of the inner surface of the hollow fiber membrane that is not covered by the potting agent added in the next step) is 20 cm ² . Fill the case, fix both ends of the hollow fiber membrane to the ends of the stainless steel case by potting, and cut a part of the end of the potting agent to open both ends of the hollow fiber membrane, creating a hollow fiber membrane module. It was set at 19. The air permeation rate and water vapor permeation rate in the obtained hollow fiber membrane module were measured. The results are shown in Table 2. The air permeation rate during drying was 0.0 mL/cm ² /min/MPa. The rate of performance decline in water vapor recovery rate when the dry air temperature ranged from 60°C to 110°C was 7.9%, and a performance decline in water vapor permeability was confirmed under the high temperature condition of 110°C.

(Comparative Example 7)
A hollow fiber membrane module 20 was obtained by conducting the same experiment as in Example 4, except that polyvinylpyrrolidone ("K30" manufactured by BASF) was used instead of the vinylpyrrolidone/vinyl acetate random copolymer. The air permeation rate and water vapor permeation rate in the obtained hollow fiber membrane module were measured. The results are shown in Table 2. The air permeation rate during drying was 510 mL/cm ² /min/MPa. Additionally, water vapor permeability was not measured due to the high air permeation rate of the membrane and the loss of feed air.

(Comparative example 8)
A hollow fiber membrane module 21 was obtained by conducting the same experiment as in Example 4, except that polyvinylpyrrolidone ("K90" manufactured by BASF) was used instead of the vinylpyrrolidone/vinyl acetate random copolymer. The air permeation rate and water vapor permeation rate in the obtained hollow fiber membrane module were measured. The results are shown in Table 2. The air permeation rate during drying was 510 mL/cm ² /min/MPa. Additionally, water vapor permeability was not measured due to the high air permeation rate of the membrane and the loss of feed air.

10: X-axis of finger void structure 20: Y-axis of finger void structure 30: Near inner surface of hollow fiber membrane cross section 40: Gap area in the center of hollow fiber membrane cross section 50: Near outer surface of hollow fiber membrane cross section 60: Air flow meter 70 : DRY gas inlet 80 : WET gas outlet 90 : Hollow fiber membrane module 100 : DRY gas outlet 110 : Temperature/humidity measurement point 120 : WET gas inlet 130 : Humidifier 140 : Air flow meter 150 : Pressure gauge 160 : Plug 170 : DRY gas inlet 180 : Hollow fiber membrane module

Claims (5)

A humidifying hollow fiber membrane, wherein at least a portion of the surface of the humidifying hollow fiber membrane is coated with a copolymer consisting of a hydrophilic unit and a hydrophobic unit,
the hydrophilic unit contains vinylpyrrolidone,
The hydrophobic unit includes a vinyl carboxylate unit, and the vinyl carboxylate unit has 1 to 4 carbon atoms at the end of the side chain,
The mole fraction of the hydrophilic unit to the entire copolymer is 50% or more and 70% or less,
the hollow fiber membrane contains a polysulfone-based polymer and polyvinylpyrrolidone, and
A humidifying hollow fiber membrane having a finger void structure when the membrane structure in a cross-sectional direction perpendicular to the longitudinal direction of the hollow fiber membrane is observed at a magnification of 1000 times using an electron microscope. When air at a temperature of 25°C and a pressure of 50 kPa is applied from the inside to the outside of a dry humidifying hollow fiber membrane, the air permeation rate is 2.5 mL/min/cm ² /MPa or more and 300 mL/min/cm ² / The hollow fiber membrane for humidification according to claim 1, which has a pressure of MPa or less. The hollow fiber membrane for humidification according to claim 1 or 2, wherein the content of polyvinylpyrrolidone in the hollow fiber membrane is 5% or less. The hollow fiber membrane for humidification according to any one of claims 1 to 3, wherein the hollow fiber membrane has an inner diameter of 500 μm or more and 1000 μm or less, and a membrane thickness of 60 μm or more and 200 μm or less. A hollow fiber membrane module equipped with the humidifying hollow fiber membrane according to any one of claims 1 to 4 .

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